Abstract
Fracture grouting has been a mitigation measure widely used against seepage in the Yellow River Embankment. However, there is currently a lack of systematic investigations studying the anti-seepage effect of the fracture grouting employed in this longest river embankment in China. Therefore, in this work, laboratory and in situ experiments are carried out to investigate the reinforcement effect of fracture grouting in the Jinan section of the Yellow River Embankment. In particular, laboratory tests concentrate on studying the optimum strength improvement for cement–silicate grout by varying the content of backfilled fly ash and bentonite as admixtures. Mechanical strength and Scanning Electron Microscope photographs are investigated for assessing the strength and compactness improvement. Subsequently, based on the obtained optimum admixtures content, in situ grouting tests are carried out in the Jinan section of the Yellow River Embankment to evaluate the reinforcement and lapping effect of fracture grouting veins, where geophysical prospecting and pit prospecting methods are employed. Laboratory results show that, compared with pure cement–silicate grouts, the gelation time of the improved slurry is longer and gelation time increases as fly ash content increases. The optimum mixing proportion of the compound cement–silicate grout is 70% cement, 25% fly ash, and 5% bentonite, and the best volume ratio is 2 for the investigated cases. Geophysical prospecting including the ground penetrating radar and high-density resistivity method can reflect the lapping effect of fracture grouting veins on site. It shows that the grouting material mainly flows along the axial direction of the embankment. The treatment used to generate directional fracture is proved to be effective. The injection hole interval distance is suggested to be 1.2 m, where the lapping effect of the grouting veins is relatively significant. For the investigated cases, the average thickness of the grouting veins is approximately 6.0 cm and the corresponding permeability coefficient is averagely 1.6 × 10−6 cm/s, which meets the anti-seepage criterion in practice.
Highlights
The Yellow River Embankment is the longest river embankment in China, and is mainly constructed of Yellow River alluvial soils, i.e., silt with low surface strength, high porosity, and drastic capillarity
The results from the GPR and high-densityresistivity resistivitymethod method (HDRM) tests in the axial direction are shown in Figures 11 and 12 respectively
In order to investigate grouting material and the anti-seepage effect of fracture grouting employed in the Yellow River Embankment, laboratory and in situ experiments were carried out to research the reinforcement effect of fracture grouting in the Jinan section of the Yellow River Embankment
Summary
The Yellow River Embankment is the longest river embankment in China, and is mainly constructed of Yellow River alluvial soils, i.e., silt with low surface strength, high porosity, and drastic capillarity. Many scholars [1,2,3] have investigated the Yellow River Embankment from different points of view. Seepage-induced instabilities such as infiltration, piping, and leakage frequently occurred in the Yellow River Embankment during its long-term operation period, mainly due to its unfavorable soil properties, animal interference, and water level change [4]. Among the potential seepage control methods, fracture grouting has been developing rapidly recently due to its low cost. More than 3000 dangerous reservoirs and 2000 km of embankments have been reinforced with fracture grouting in the past 20 years [6]. Researchers have carried out a series of studies on grouting materials [7,8,9], grouting mechanism, and fluid flow [10,11] against seepage through indoor experiments and theoretical analysis
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